Blighttown Skip

From SpeedSouls - A Dark Souls Speedrunning Wiki

The Blighttown Skip is a sequence break in Dark Souls that allows the player to skip the area Blighttown entirely by going out of bounds in New Londo Ruins and dropping down from above into the tunnel of Quelaag's Domain by abusing the Fall Control Quitout mechanic. It was discovered by ImmersedCimp in September 2016. A faster version of Blighttown Skip using Area Transition Clipping was discovered in February 2019.